(i) Field of the Invention
The present invention relates to a slipping clutch mechanism suitable for use in stationary head fans which provide a gyratory distribution pattern of air flow.
(II) Description of the Prior Art
The specification of Australian Pat. No. 459,701, describes and claims a fan in which the fan head remains stationary but which is capable of delivering air in a substantially gyratory distribution pattern. The term "gyratory distribution pattern" is intended to indicate an air flow distribution pattern which is substantialy the same as that produced by a fan with a gyratory head, except that the flow is more laminar and less spiral. The fan described in the above patent specification is broadly defined as comprising a fan blade assembly, an electric motor for driving the fan blade assembly, means to render the air flow from the blade assembly wholly axial, and an air directing grille mounted in the path of the flow of air from the blade assembly and said means, and driven by the motor to rotate at a speed less than the blade assembly speed, said grille including a plurality of louvres arranged parallel to and at different acute angles to the flow of air, such that the air flow is directed by the grille in a substantially gyratory distribution pattern.
The fan particularly described in the specificaton of Australian Pat. No. 459,701 includes a clutch mechanism which operates to disconnect drive to the grille in the event that rotation of the grille is obstructed. The mechanism described in the specification of Australian Pat. No. 459,701 comprises three spring steel leaf springs which extend rearwardly from equiangularly disposed locations at the rear of a central hub incorporated into the grille, the grille, and thus the hub, also being mounted for movement coaxially of a drive shaft of the electric motor for the fan. The latter motor drive shaft is fitted with a coaxial clutch ring and the grille is mounted such that it can be moved from a forward non-driving disposition, at which free rear ends of the springs are forwardly disposed of and clear from the clutch ring, to a rearward location to engage drive to the grille. During this rearward movement, the free ends of the springs initially engage a peripheral, sloping, cam surface on the forward end of the clutch ring to force the free ends radially apart, whereupon, after further rearward movement the free ends ride over this cam surface to be engaged in a peripheral annular groove on the clutch ring. The groove is sinuously configured at its root so as to define a plurality of radially inwardly extending notches therein, these notches being equispaced around the axis of the drive shaft and being separated by radially outwardly extending crests in the root. The free rear ends of the springs enter appropriately positioned ones of these notches and so key the hub and clutch ring together to rotate the grille together with the drive shaft. In the event that rotation of the grille is obstructed whilst the clutch mechanism is so engaged, the drive shaft can still continue to rotate without transmitting excessive driving force to the grille, the free ends of the springs merely being repetitively forced outwardly against the resilient bias thereof, by camming action as the free ends are engaged by successive crests of the groove root. Whilst this clutch mechanism is quite satisfactory in use, it does suffer the disadvantage that it is relatively complex in construction, for an item intended to be mass-produced, so that there is an undesirable cost component introduced into the overall price of the fans due to the labour intensive nature of the assembly operations of the clutch. In particular, in the construction described in the specification of Australian Pat. No. 459,701 assembly of the clutch mechanism requires the following operations:
Firstly, the leaf springs are individually screwed onto the hub and the clutch ring is assembled onto the motor drive shaft. Then, with the hub located in position to extend coaxially of the drive shaft and with the free end portions of the springs fitted into the notches of the grooves of the clutch ring, a screw is inserted through an opening in a transverse wall of the hub to extend into a threaded bore in the shaft, this being to prevent the grille from leaving the shaft under forward pressure of air displaced by the fan.
It will be appreciated that these assembly operations are difficult to automate.
Aside from the above, the mechanism described in the specification of Australian Pat. No. 459,701 may occasionally fail by virtue of the working loose of the screw holding the hub to the shaft, and whilst this difficulty may be avoided by routine inspection, the arrangement is not so completely satisfactory as is desirable.